Collapsible revolving doors are provided, in order to provide a clear passage from a building in an emergency situation. In an emergency, a rigid non-collapsing revolving door can easily become blocked or jammed by the pressure of people hurrying to get through it. In such a situation, a collapsible revolving door will collapse, providing a clear, unobstructed passage, which enables a far greater volume of people to pass through it.
Many different types of mechanism have been proposed to enable revolving doors to collapse. Many of these mechanisms are complex, and suffer from numerous disadvantages. For example, some mechanisms are costly while other mechanisms are difficult and time consuming to install. In many mechanisms the revolving door is not very rigid and it is difficult to adjust the force at which the individual leaves will collapse.
U.S. Pat. No. 2,043,780 (Simpson) is an old disclosure of a collapsible revolving door mechanism, and is nearly 50 years old. Each door wing or leaf is attached to top and bottom discs. For attachment to each disk, three pins are secured to each door leaf. A first pin is disposed adjacent the radially inner edge of the door, and is disposed in a generally V-shaped slot that faces upwards. In the normal position, this first pin is at the bottom of the V-shaped notch or recess. Two further pins, larger than the first pin, are located radially outwards relative to the first pin, on either side of the door leaf. They both engage an arcuate slot centered on the first pin. The slot has a width slightly less than the main body of the further pins, and these two pins have flattened faces adapted to engage this slot. At either end of the slot, there is an enlarged bore corresponding to the size of each of these two other pins. A spring loaded latch-type mechanism retains each door leaf in its usual position. When subject to excessive force, this latch mechanism is overcome, and the particular door leaf can collapse relative to the other leaves. Upon collapse, the leaf first pivots about the first inner pin. It pivots about this pin, until one of the second, larger pins reaches the end of the arcuate slot. At this point, the other of the second larger pins is free to exit the arcuate slot. Consequently, the leaf continues to pivot, but the pivot action now occurs about the pin that has reached its respective enlarged ball at the end of the slot. The second large pin leaves the slot, and the first pin also leaves its V-shaped notch or recess. After a certain amount of movement, the pin in the bore will become fully engaged with the bore, as its flattened face is turned away from the slot, so that it securely retains the leaf.
While this type of mechanism has some advantages over other mechanisms, it is relatively complex and costly. It relies on six separate pins for each leaf, resulting in a total of 24 pins for a four leaf door. Also, assembly and disassembly of this sort of mechanism is quite difficult, and frequently special means have to be provided for this. A number of other patents disclose this type of mechanism and to distinguish it from other collapse mechanisms, it will be described as a "3-pin mechanism".
U.S. Pat. No. 2,539,790 (Nordin) is another disclosure of a "3-pin mechanism". The arrangement here is somewhat different in that the pins are fixed in position, and each door is provided with a span arm, including notches adapted to engage these pins. Additionally, each span arm has a pin located in a cam track, to control the motion of the door leaf. Again, in a normal position, each span arm is retained by a spring biased latch mechanism against a first pin. In response to abnormally large forces, each door leaf can collapse. For collapse in one direction, the leaf pivots about the first pin until a notch engages another pin. At this point, the pin attached to the door has reached the beginning of a circular section of the cam track centered on the second pin. Consequently, the leaf can continue to rotate or collapse about the second pin. Here again, the overall construction is complex and requires numerous different components. Assembly and disassembly would be quite complex.
U.S. Pat. Nos. 3,762,098 and 3,793,773 (both in the name Sheckells) both disclose similar revolving door mechanisms, including a 3-pin collapse pin mechanism. Each door or door leaf is mounted via a small pin and two larger pins. Each of the larger pins is generally cylindrical, with one face formed as part of a circle centered on the small pin. In the normal position,these faces of the larger pins are against a corresponding curved surface of a hanger disk. A latch-type detente mechanism retains the door in its usual position. In response to excessive force, the door first starts to pivot about the small pin. This motion continues until one of the larger pins enters a respective, corresponding cylindrical recess. At this stage, the door then pivots about this larger pin. The second larger pin is then free, as is the small pin. Consequently, the door can rotate unobstructed about the larger pin. Here, again, the arrangement of larger pins with bearing surfaces and corresponding cylindrical recesses is such that after rotation commences around one of the larger pins, that larger pin is retained in its cylindrical recess and cannot leave it until the door is returned to its normal position. This construction, like many of the other known constructions, is somewhat complex. The arrangement for attachment and removal of the individual doors or door leaves is complex. Either special screws or removable portions are needed to enable fitting and removal of the door leaves.
Applicant's earlier U.S. Pat. No. 3,782,035 is of some interest, in that it discloses a door mechanism effectively provided with two separate pivot locations for each door. One pivot location being for collapse in one direction and the other pivot location being for collapse in the other direction. At each end, each door leaf is provided with two seats for receiving spring loaded balls. The engagement of a pair of spring loaded balls at either end of the door leaf locates it in position. In response to excessive force, one ball seat at the top and one at the bottom become disengaged from their respective balls, to permit rotation of the door about the remaining two engaged balls and ball seats. While this provides a collapsible door structure, it suffers from some disadvantages. The doors are retained in position solely by the pressure of the balls on the ball seats. Thus, to secure the doors, the springs acting on the balls have to provide considerable pressure. This pressure or force has to be transmitted through the central shaft of the door from top to bottom, and consequently, this shaft is under considerable stress. Assembly and disassembly is complicated and requires tensioning the shaft to apply the pressure to the balls. Also, a single door leaf cannot readily be removed. Since the doors are only located by means of balls acting in ball seats, a rigid structure is only obtained with larger forces.
For a revolving door, including a collapse mechanism, it is desirable that the structure should be as simple as possible. The arrangement should be such as to permit the door to be readily assembled and disassembled. Also, it should permit any one individual door or door leaf to be quickly and easily removed or installed, without affecting the remainder of the doors. Also, the door structure should be such as, in normal use, to provide a rigid, stable structure. Many known mechanisms rely upon some type of spring loaded detent mechanism, in which a latch is displaced sideways from a seat. The latch has to be arranged to be displaced sideways, to accommodate movement in two different directions, for the two possible collapse modes. Such an arrangement inherently leads to a structure which is not that rigid, as the latch is either a ball or tapered wedge resting in corresponding seat. It is desirable that the latch mechanism provide a more positive engagement of each door leaf in its usual position.